The desirability of employing fibrous reinforcing material in concrete and other cementitious building materials has been known for a number of years. In many instances, the use of fiber reinforcing material reduces or eliminates the need for reinforcing rods while maintaining improved shrinkage crack resistance. The fiber-reinforced material can often be formed at lower cost than similar material containing steel rod or wire mesh reinforcement. Where concrete is used in applications that are exposed, such as roadways, the presence of the fibers at the surface exposed to the roadway also provides improved wear resistance.
One difficulty that has inhibited use of fiber reinforced materials is the tendency of the fibers to adhere to each other and form balls after being delivered into construction mixtures when they are not fully wetted by the construction mixture. The result of balling is poor matrix to fiber bonding and a corresponding decrease in strength of the finished construction material. Moreover, where the balls are of significant size, a partial void in the material is formed which results in a defect or weak spot in the finished material.
Cellulose and mineral fibers are commonly used to modify the rheological properties of liquid systems, including those based on cement and water, and those based on bitumen. The fibers have a gelling or thickening effect on these systems which may include, for example, a cement-based tile adhesive, concrete, or a bituminous road surfacing compound. Cellulose and mineral fiber usage has increased partly due to the demise of asbestos fiber.
Cellulose fiber is often supplied in dry, compressed bales which may be from about 1 Kg to about 400 Kg in weight and have a density of from about 0.4 to about 0.9 g/cc. To be effective as a reinforcing material, the fibers must be delivered into the mixture and be dispersed therein. Cellulose fiber is also supplied in rolls. One problem in the state of the art is the length of time required for uniform dispersion of the fibers once they are delivered into the construction mixture.
There are three main methods for adding fiber to cementitious and other construction mixtures. In one method, bales may be added directly to a mixer. Thus, in the case of hot bitumen mixtures, the whole bale including polyethylene packaging is added, the plastic quickly dissolving into the hot liquid bitumen. Alternatively, and particularly in the use of dry powder mixes, the fiber is emptied from the package directly into the mixer. Or, the fiber is supplied via a hopper and screw arrangement, possibly after a weighing operation to obtain the exact quantity required for a batch. These prior art methods are labor intensive, and often require an operator to work very close to mixing machinery. There are also the environmental problems of dust, fumes and noise for methods that require complicated procedures and extensive mixing times.
U.S. Pat. Nos. 1,048,913; 1,349,901; 1,571,048; 1,633,219; 1,913,707; 2,377,484; and 2,677,955 relate to the use of various materials including fibers in concrete. Early efforts were aimed at improving crack resistance and improving the energy absorption of concrete masses. U.S. Pat. Nos. 4,188,454; 4,287,365; 4,287,020; 4,310,478; 4,369,201; 4,4,400,217; 4,483,727; 4,524,101; 4,524,101; 4,861,812; 4,985,119; 4,968,561; 5,000,824; 5,196,061; 5,362,562; 5,385,978; 5,399,195; and 5,453,310, 5,643,359, 5,897,701, all of which are hereby incorporated by reference in their entirety, relate to various efforts to provide improved reinforced materials.